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My band uses a very simple in-ear-monitoring set-up in the practice room where we are taking advantage of the 4 AUX channels on the huge audio mixer there. We do use cheap headphone amps which cannot boost the incoming signal of the aux outputs enough, so we have to crank the aux output knobs all the way to max. But then it seems that the click is audible on the main mix as well, though it is only to be audible on the in-ears.

How is this 'signal spillover' possible? Might it be how the audio mixers are constructed? We are wondering if it could happen on better mixers at concert venues as well, then we would have to change our set-up, which would cost time and money.

  • Are you saying that the click on the main mix comes and goes when you move the aux output knobs? Presumably you can check that out with no input from your instruments and mikes all disconnected. A mixer shouldn't have any unintended spill between channels - you need to systematically check out why the click is getting to the wrong place. Connect just one thing at a time and play with the faders, till you find it. – user19146 Jun 13 '17 at 18:29
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    When you're hearing the click in the mains, is it fairly quiet or is it about as loud as the click in the auxes? Also, cheap headphone amps are good enough for monitoring and not that hard to come by. You really shouldn't crank levels inside a mixer if you can avoid it, and you shouldn't plug headphones straight into aux outputs. If the auxes are balanced then you are really messing things up. – Todd Wilcox Jun 13 '17 at 18:47
  • I will check it again on thursday when we practice the next time but as I recall I tried that already. And it seems to only occur when the AUXs are maxed out. – juliusklaus Jun 13 '17 at 18:48
  • The click is very quiet but audible during quiet passages. Also we checked already for the headphones being accidentally recorded by a mic. Not the case. – juliusklaus Jun 13 '17 at 18:50
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With all respect to Alephzero's comment, pretty much all mixers have what you might call "spillover" between adjacent channels and among different busses. It's critical to not have any coupling between inputs and outputs (channels and busses) because that causes in the box feedback.

You can't make electronics with zero coupling, and when you crank a channel or bus level you are creating a huge disparity in power and the resulting EM fields. Pretty much no circuit in audio is designed to work at the outer limits of its settings.

Somehow I didn't notice that you are already using headphone amps. I'm a little worried about how loud you might be making those amps if they can't get the headphone level of in-ears high enough on their own. Ideally the aux master level controls should be set of around unity gain.

Your next step should be to check the kind of output and nominal output level for the aux sends and then the kind of input and nominal input level for the headphone amps. The best combination would be that they are both TRS balanced line level. The auxes are almost certainly mono TRS balanced, so if the headphone amps are stereo TRS and you're using a TRS cable to connect the two, that's a major configuration error that is probably causing your problem.

  • Thank you for your effort! That it is impossible to build electronics with zero coupling is a very interesting and valuable piece of information for me. You might be right with checking back on the initial connection between AUX and mic-amp. I will do that on thursday and will let you guys know how it turned out. I will edit the question to include additional information I will gain through this then. Thank you! – juliusklaus Jun 13 '17 at 21:32

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